Conductive oxide film, display device, and method for forming conductive oxide film

ABSTRACT

One embodiment of the present invention provides a conductive oxide film having high conductivity and high transmittance of visible light. The conductive oxide film having high conductivity and high transmittance of visible light can be obtained by forming a conductive oxide film at a high substrate temperature in the film formation and subjecting the conductive oxide film to nitrogen annealing treatment. The conductive oxide film has a crystal structure in which c-axes are aligned in a direction perpendicular to a surface of the film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a conductive oxide film, a displaydevice, and a method for forming a conductive oxide film.

The present invention relates to a conductive oxide film having acrystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film, and a method for forming theconductive oxide film. In addition, the present invention relates to adisplay device using such a conductive oxide film.

2. Description of the Related Art

Recently, touch panels having a multi-touch function have widespreadrapidly in accordance with the increasing demand for smartphones ortablet PCs. Transparent conductive oxide films are utilized in touchpanels, thin-film solar cells, and particle moving type electronic paperusing electronic liquid powder. The demand for high-quality transparentconductive oxide films is expected to increase, and the market of thefilms will expand in the future.

Materials that are used for the transparent conductive oxide films areroughly classified into crystalline materials and amorphous materials.Examples of the crystalline materials are indium tin oxide (ITO) andzinc oxide (ZnO), and an example of the amorphous materials is indiumzinc oxide.

ITO is the most general material of the transparent conductive oxidefilm, and a sputtering method is the most general method for forming thetransparent conductive oxide film. For the transparent conductive oxidefilms, a reduction in cost of the film formation and the material aswell as several properties such as high transmittance of visible light,high conductivity, and low electric resistance is required.

As a factor for indicating the conductivity of the transparentconductive oxide films, sheet resistance is used. For the uses ofelectronic paper, a sheet resistance of approximately 300 Ω/□ to 400 Ω/□is enough for operation; however, a sheet resistance of 200 Ω/□ or loweris desired for the uses of touch panels.

The sheet resistance depends on carrier density and mobility. As thesheet resistance becomes lower, the carrier density becomes higher orthe mobility becomes higher, which means higher conductivity. Further,the sheet resistance depends on thickness. For example, the sheetresistance of an ITO film with a thickness of 30 nm is approximately 100Ω/□, and that with a thickness of 200 nm is approximately 10 Ω/□.

In Patent Document 1, a method for forming a dense ZnO film havingcrystallinity is disclosed.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. 2009-57605

SUMMARY OF THE INVENTION

Transparent conductive oxide films are required to have highconductivity and high transmittance of visible light.

In order to have high transmittance of visible light, the transparentconductive oxide films need to have a band gap that does not exist in avisible light range of from 380 nm to 780 nm (3.26 eV to 1.59 eV). Ifthe transparent conductive oxide films have a band gap of about 3 eV,absorption of light in the visible light range can be reduced in thefilms.

In order to have high conductivity, the transparent conductive oxidefilms need to have a carrier density that is lower than the carrierdensity of metal (2.0×10²¹ cm⁻³ or more) and is high enough(approximately 1.0×10²⁰ cm⁻³ to 1.0×10²¹ cm⁻³). If the transparentconductive oxide film has a carrier density higher than or equal to thecarrier density of metal, reflection of light in the visible light rangeis increased, so that the light transmittance is decreased.

In other words, the tradeoff for either one of high conductivity andhigh transmittance of visible light in the transparent conductive oxidefilm causes an adverse effect. Higher conductivity causes lower lighttransmittance. In addition, higher light transmittance enhances aninsulating property.

It is an object to provide a conductive oxide film having highconductivity and high transmittance of visible light.

To improve both the light transmittance and the conductivity of aconductive oxide film, the conductive oxide film is formed to have acrystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film and then subjected to nitrogenannealing treatment.

One embodiment of the present invention disclosed in this specificationis a conductive oxide film having a crystal structure in which c-axesare aligned in a direction perpendicular to a surface of the film. Thec-axes of crystal parts included in the conductive oxide film arealigned in a direction perpendicular to the surface of the film. Notethat in this specification, the “conductive oxide film having a crystalstructure in which c-axes are aligned in a direction perpendicular to asurface of the film” may be referred to as a “CAAC (c-axis alignedcrystalline)-conductive oxide film.”

One embodiment of the present invention disclosed in this specificationis a conductive oxide film having a crystal structure having adiffraction peak obtained by X-ray diffraction measurement at 31°.

Note that the fact that the diffraction peak obtained by X-raydiffraction measurement is in the vicinity of 31° can be interpreted tomean that the c-axes of crystal parts are aligned in a directionperpendicular to the surface of the film.

The above-described conductive oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film has a band gap of preferably larger than or equal to 2.5 eV,further preferably larger than or equal to 3.0 eV.

The conductive oxide film having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film hasexcellent light transmittance.

Although the mechanism of the excellent light transmittance of theconductive oxide film having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film isunclear, a possible reason of the excellent light transmittance is arelatively low density of defect states in the band gap of theCAAC-conductive oxide film compared with an amorphous conductive oxidefilm. The low density of defect states in the band gap leads to thesuppression of absorption of light in the visible light range due todefect states. Accordingly, transmittance of visible light can beincreased.

Further, another possible reason is that the conductive oxide filmhaving a crystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film tends to have a larger band gapthan conductive oxide films having the other crystal structures, anamorphous conductive oxide film, and the like. Since a larger band gapenables transmission of light in a wider range of wavelength, theconductive oxide film can transmit much light in the visible light rangeof 380 nm to 780 nm. Accordingly, transmittance of visible light can beincreased.

The above-described conductive oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film preferably has a sheet resistance of lower than or equal to 40Ω/□.

The above-described conductive oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film particularly preferably has a sheet resistance of lower than orequal to 40 Ω/□ when having a thickness of more than or equal to 1 nmand less than or equal to 100 nm.

The conductive oxide film having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film hasexcellent conductivity.

Although the mechanism of the excellent conductivity of the conductiveoxide film having a crystal structure in which c-axes are aligned in adirection perpendicular to a surface of the film is unclear, a possiblereason of the excellent conductivity is high mobility of the conductiveoxide film. Since the conductive oxide film having a crystal structurein which c-axes are aligned in a direction perpendicular to a surface ofthe film can have a relatively low density of defect states in the bandgap, the number of impurity scattering factors that cause a reduction ofmobility can be small.

In the case of providing a function of sensing a touch position (touchpanel) outside a display device such as a liquid crystal display deviceor an organic EL display device or an electronic device, the conductiveoxide film having a crystal structure in which c-axes are aligned in adirection perpendicular to a surface of the film can be used as anelectrode for sensing the touch position in the touch panel. Theconductive oxide film, which has high conductivity and hightransmittance of visible light, contributes to an increase in thesensing accuracy of the touch position in the touch panel.

For example, in the case of forming a touch panel using one substrateand forming a conductive oxide film over the substrate, a touch positioncan be sensed by a change in current flowing through the conductiveoxide film.

Further for example, in the case of forming a touch panel using twosubstrates and forming a first conductive oxide film over a firstsubstrate and a second conductive oxide film over a second substrate, atouch position can be sensed by contact between the first conductiveoxide film and the second conductive oxide film.

Further for example, in the case of forming a touch panel using twosubstrates and forming a first conductive oxide film over a firstsubstrate and a second conductive oxide film over a second substrate, atouch position can be sensed by a change in capacitance generatedbetween the first conductive oxide film and the second conductive oxidefilm.

Even in the case of providing a function of sensing a touch positioninside a display device or an electronic device, the conductive oxidefilm having a crystal structure in which c-axes are aligned in adirection perpendicular to a surface of the film can be used as anelectrode for sensing the touch position.

For example, two substrates between which a liquid crystal layer issandwiched are used. In addition, a first conductive oxide film and anelectrode for controlling the liquid crystal layer (pixel electrode) areformed over one substrate; thus, the electrode for sensing the touchposition and the electrode for controlling the liquid crystal layer canbe formed over the same substrate. Further, a second conductive oxidefilm and an electrode controlling the liquid crystal layer (commonelectrode) are formed over the other substrate; thus, the electrode forsensing the touch position and the electrode for controlling the liquidcrystal layer can be formed over the same substrate. Since theelectrodes for sensing the touch position and the electrodes forcontrolling the liquid crystal layer are placed inside a pixel of aliquid crystal display device, the thickness of the liquid crystaldisplay device can be made small, and the performance of the liquidcrystal display device can be increased. Further, the first conductiveoxide film can also serve as a pixel electrode, or the second conductiveoxide film can also serve as a common electrode.

Further for example, two substrates between which a light-emitting layeris sandwiched are used. In addition, a first conductive oxide film isformed over one substrate, and a second conductive oxide film is formedover the other substrate. Thus, an electrode for sensing the touchposition and an electrode for controlling the light-emitting layer canbe placed inside a pixel of an organic EL display device.

One embodiment of the present invention disclosed in this specificationis a method for forming a conductive oxide film including the steps of:forming a conductive oxide film over a substrate by a sputtering methodat a substrate temperature of 200° C. or higher; and performing nitrogenannealing treatment on the conductive oxide film.

One embodiment of the present invention disclosed in this specificationis a method for forming a conductive oxide film including the steps of:forming a conductive oxide film over a substrate by a sputtering methodin an atmosphere including an argon gas at a substrate temperature of200° C. or higher; and performing nitrogen annealing treatment on theconductive oxide film.

In the formation methods, as the amount of an argon gas added in thefilm formation is larger, the conductivity of the conductive oxide filmhaving a crystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film is higher.

In the formation methods, as the amount of an oxygen gas added in thefilm formation is larger, the conductive oxide film is likely to includemore CAAC parts. That is, as the amount of an oxygen gas added in thefilm formation is larger, the diffraction peak in the vicinity of 31°,which is obtained by X-ray diffraction measurement, is sharper. Notethat in this specification, “a conductive oxide film is likely toinclude more CAAC parts” means “a conductive oxide film is likely toinclude more crystal parts whose c-axes are aligned in a directionperpendicular to a surface of the film”.

It is preferable to appropriately adjust the amount of an oxygen gas andthe amount of an argon gas which are added in the formation of theconductive oxide film, in consideration of the conductivity and thetransmittance of visible light.

In the formation methods, the ratio of the amount of the added oxygengas to the amount of the added argon gas in the film formation isparticularly preferable 3:7.

In the formation methods, the substrate temperature in the filmformation is preferably higher than or equal to 200° C., furtherpreferably higher than or equal to 400° C.

In the formation methods, as the substrate temperature in the filmformation is higher, the conductive oxide film is likely to include moreCAAC parts. The conductive oxide film including more CAAC parts can havehigher transmittance of visible light and higher conductivity.

In the formation methods, nitrogen annealing treatment is performed onthe formed conductive oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of thefilm. The nitrogen annealing treatment allows the conductive oxide filmhaving a crystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film to have higher conductivity. Thatis, the nitrogen annealing treatment can reduce the sheet resistance ofthe conductive oxide film having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film.

By the nitrogen annealing treatment, oxygen vacancies in the conductiveoxide film having a crystal structure in which c-axes are aligned in adirection perpendicular to a surface of the film are increased. Thedensity of free electrons serving as carriers for electric conduction isincreased, causing an increase in the carrier density in the conductiveoxide film. In other words, the nitrogen annealing treatment increasesthe conductivity of the conductive oxide film.

In the formation methods, the temperature in the nitrogen annealingtreatment is preferably higher than or equal to 350° C., furtherpreferably higher than or equal to 450° C. By increasing the temperaturein the nitrogen annealing treatment, higher conductivity of theconductive oxide film having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film can beachieved.

The time for the nitrogen annealing treatment is preferably about onehour.

The nitrogen annealing treatment may be performed in a mixed gasatmosphere of a nitrogen gas and a rare gas.

The nitrogen annealing treatment is preferably performed in anatmosphere not including an oxygen gas.

In the formation methods, the light transmittance and conductivity ofthe conductive oxide film tend to be controlled by the substratetemperature in the film formation, the amount of an oxygen gas added inthe film formation, the amount of an argon gas added in the filmformation, whether the nitrogen annealing treatment is performed afterthe film formation, the temperature of the nitrogen annealing treatment,and the like.

In the formation methods, by setting the substrate temperature in thefilm formation and the temperature in the nitrogen annealing treatmentperformed after the film formation at high temperatures, the conductiveoxide film with high quality can be obtained easily.

The conductive oxide film formed by any of the above-described formationmethods solves the above-described problem.

Note that in this specification, a simple term “perpendicular” includesa range from 85° to 95°.

A conductive oxide film having high conductivity and high transmittanceof visible light can be obtained in the following manner: a conductiveoxide film is formed at a high substrate temperature and the film isthen subjected to nitrogen annealing treatment. In addition, aconductive oxide film having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film can beobtained.

By appropriately selecting the amount of an argon gas added in the filmformation, a conductive oxide film with higher conductivity can beobtained.

By appropriately selecting the amount of an oxygen gas added in the filmformation, a conductive oxide film with higher crystallinity can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B show X-ray diffraction data of conductive oxide films;

FIGS. 2A and 2B are cross-sectional TEM photographs of conductive oxidefilms;

FIG. 3 shows X-ray diffraction data of conductive oxide films;

FIG. 4 shows X-ray diffraction data of conductive oxide films;

FIGS. 5A and 5B each show X-ray diffraction data of conductive oxidefilms;

FIGS. 6A and 6B illustrate an organic EL display device;

FIGS. 7A and 7B illustrate an organic EL display device;

FIGS. 8A to 8C illustrate an electronic device;

FIGS. 9A to 9C illustrate a touch panel; and

FIGS. 10A to 10C illustrate a touch panel

FIG. 11 shows X-ray diffraction data of conductive oxide films.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described with reference to the accompanyingdrawings. Note that the invention is not limited to the followingdescription, and it will be easily understood by those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the invention. Therefore, the inventionshould not be construed as being limited to the description in thefollowing embodiments. Note that in the structures of the inventiondescribed below, the same portions or portions having similar functionsare denoted by the same reference numerals in different drawings, anddescription of such portions is not repeated.

Embodiment 1

In this embodiment, the case of forming a conductive oxide film under acondition in which the percentage of an argon gas in film formation is100% is described with reference to FIGS. 1A and 1B and Table 1.

In this embodiment, the case of forming an indium zinc oxide film isdescribed as an example.

A method for forming the indium zinc oxide film and conditions for thefilm formation are described. The indium zinc oxide film was formed by asputtering method. The conditions are described below.

A target with a composition of In:Zn=2:1 (a molar ratio ofIn₂O₃:ZnO=1:1) was used. The film formation was performed under twoconditions of the substrate temperature, 200° C. and 400° C. Thereaction pressure was 0.4 Pa, and the DC power was 0.5 kW.

Note that nitrogen annealing treatment was not performed after the filmformation.

Table 1 shows the measurement results of the sheet resistances of theindium zinc oxide films formed under the above-described conditions.

TABLE 1 Indium zinc oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmArgon:Oxygen 100%:0% 100%:0% Substrate temperature 200° C. 400° C.Nitrogen annealing treatment Not performed Not performed Sheetresistance [Ω/□] 47.1 37.2

The sheet resistances of the indium zinc oxide films were measured bythe following procedures. First, indium zinc oxide films each having athickness of approximately 100 nm were formed over substrates under theabove-described conditions. Then, the sheet resistance of the indiumzinc oxide film formed at the substrate temperature of 200° C. and thesheet resistance of the indium zinc oxide film formed at the substratetemperature of 400° C. were measured by a four-point probe method. Notethat the measurement accuracy of a four point probe is 0.2%.

Table 1 shows very favorable measurement results of the sheetresistance: 47.1 Ω/□ in the case where the substrate temperature in thefilm formation is 200° C. and 37.2 Ω/□ in the case where the substratetemperature in the film formation is 400° C. These values are enough forthe function as conductive oxide films and are within the rangeappropriate for use in touch panels and electronic paper.

The measurement results show that the sheet resistance in the case wherethe substrate temperature in the film formation is 400° C. is lower thanthe sheet resistance in the case where the substrate temperature in thefilm formation is 200° C. This indicates that as the substratetemperature in the film formation is higher, the conductivity of theindium zinc oxide film is higher.

Note that the indium zinc oxide films formed under the above-describedconditions were not subjected to nitrogen annealing treatment after thefilm formation. If the nitrogen annealing treatment is performed on theindium zinc oxide films formed under the above-described conditions,lower sheet resistance is expected.

Next, the crystal structures of the indium zinc oxide films formed underthe above-described conditions and having excellent conductivity wereexamined.

As a measurement apparatus, a powder X-ray diffractometer (D-8 ADVANCE)manufactured by Bruker AXS was used.

FIGS. 1A and 1B show measurement results of X-ray diffraction (XRD) dataof the indium zinc oxide films formed under the above-describedconditions. The horizontal axis represents the diffraction angle (2θ(deg)), and the vertical axis represents the XRD intensity (arb. units).

Note that although arbitrary units are used in the vertical axis inFIGS. 1A and 1B, the scale of the vertical axis is common to allspectra.

FIG. 1A shows the measurement results of XRD data in the case where thesubstrate temperature in the film formation is 200° C., and FIG. 1Bshows the measurement results of XRD data in the case where thesubstrate temperature in the film formation is 400° C. In each of FIGS.1A and 1B, the upper XRD data indicates the results in the case whereheat treatment is performed in a vacuum atmosphere after the formationof the indium zinc oxide film, and the lower XRD data indicates theresults in the case where heat treatment is not performed after theformation of the indium zinc oxide film.

From FIGS. 1A and 1B, it can be found that the diffraction peaksobtained by XRD measurement are in the vicinity of 31°.

Thus, in spite of the percentage of an argon gas in the film formationof 100%, by forming an indium zinc oxide film by a sputtering methodunder the conditions of the substrate temperature of 200° C. or higher,the indium zinc oxide film can have a crystal structure in which c-axesare aligned in a direction perpendicular to a surface of the film.

Further, the diffraction peaks in the vicinity of 31° in FIG. 1B aresharper than those in FIG. 1A, which means that the indium zinc oxidefilms formed under conditions of the substrate temperature of 400° C.are likely to include more CAAC parts than the indium zinc oxide filmsformed under conditions of the substrate temperature of 200° C.

From the above-described measurement results, it can be found that theindium zinc oxide film including more CAAC parts has higherconductivity.

The density of defect states in the band gap can be expected to decreaseas the indium zinc oxide film includes more CAAC parts.

Next, the absorption coefficient was measured. The absorptioncoefficient of an indium zinc oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film and the absorption coefficient of an indium zinc oxide filmhaving an amorphous structure, which is a comparative example, weremeasured. The values were compared.

As a measurement apparatus, SGA-4 manufactured by Bunkoukeiki Co., Ltd.was used, and as a light source, a Xe lamp was used. Note that themeasurement wavelength range was 300 nm to 1200 nm.

The absorption coefficient of the indium zinc oxide film having acrystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film was found to be 2.5×10⁻¹ cm.

The absorption coefficient of the comparative example, the indium zincoxide film having an amorphous structure, was found to be 3.0×10⁻¹ cm.

The absorption coefficient of the indium zinc oxide film having acrystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film was lower than that of the indiumzinc oxide film having an amorphous structure.

This indicates that the indium zinc oxide film having a crystalstructure in which c-axes are aligned in a direction perpendicular to asurface of the film has more excellent light transmittance than theindium zinc oxide film having an amorphous structure.

As the density of defect states is lower, the number of impurityscattering factors that cause a reduction of mobility is smaller,leading to a lower absorption coefficient. Consequently, as the indiumzinc oxide film includes more CAAC parts, the conductivity becomeshigher.

Further, as the density of defect states is lower, the absorption oflight in the visible light range due to defect states can be suppressedmore. Consequently, as the indium zinc oxide film includes more CAACparts, the transmittance of visible light becomes higher.

All the above-described measurement results suggest that as thesubstrate temperature in the film formation is higher, the indium zincoxide film is likely to include more CAAC parts and that the indium zincoxide film including more CAAC parts more easily achieves increases inboth conductivity and transmittance of visible light.

Embodiment 2

In this embodiment, the case of forming a conductive oxide film under acondition in which the percentage of an argon gas in film formation islower than or equal to 70% is described with reference to FIGS. 2A and2B, FIG. 3, FIG. 4, FIGS. 5A and 5B, FIG. 11, and Tables 2 to 7.

In this embodiment, the case of forming an indium zinc oxide film isdescribed as an example.

A method for forming the indium zinc oxide film and conditions for thefilm formation are described. The indium zinc oxide film was formed by asputtering method. The conditions are described below.

A target with a composition of In:Zn=2:1 (a molar ratio ofIn₂O₃:ZnO=1:1) was used. The film formation was performed under thefollowing two conditions of the gas ratio in film formation:thepercentage of an oxygen gas of 100% and the ratio of an argon gas:anoxygen gas=7:3. The film formation was performed under two conditions ofthe substrate temperature, 25° C. (room temperature) and 200° C. Thereaction pressure was 0.4 Pa, and the DC power was 0.5 kW.

The indium zinc oxide films used for the measurement in FIGS. 2A and 2B,FIG. 3, FIG. 4, FIGS. 5A and 5B, FIG. 11, and Tables 2 to 7 were eachformed under any of the above-described conditions.

The measurement results of the case in which nitrogen annealingtreatment was performed on the indium zinc oxide film formed under anyof the above-described conditions after the film formation are alsoshown.

FIGS. 2A and 2B are cross-sectional TEM photographs, and FIG. 3 showsmeasurement results of XRD data.

The film formation conditions of the indium zinc oxide films shown inFIGS. 2A and 2B and FIG. 3 are as follows: the composition of the targetis In:Zn=2:1, the percentage of an oxygen gas in film formation is 100%,the substrate temperature is 200° C., the reaction pressure is 0.4 Pa,and the DC power is 0.5 kW.

Note that the nitrogen annealing treatment was not performed on theseindium zinc oxide films after the film formation.

FIG. 2A is a cross-sectional TEM photograph of an indium zinc oxide filmformed in the following manner: a silicon oxynitride film is formed as abase film over a substrate, and then the indium zinc oxide film isformed over the base film of the silicon oxynitride film. FIG. 2B is across-sectional TEM photograph of an indium zinc oxide film formed inthe following manner: a silicon oxide film is formed as a base film overa substrate, and then the indium zinc oxide film is formed over the basefilm of the silicon oxide film.

As is apparent from FIGS. 2A and 2B, the formed indium zinc oxide filmseach have a crystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film. Crystal parts are neatly alignedin the perpendicular direction. Accordingly, the indium zinc oxide filmsformed under the above-described conditions are indium zinc oxide filmshaving a crystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film.

FIG. 3 shows XRD data of the indium zinc oxide films shown in FIGS. 2Aand 2B and having a crystal structure in which c-axes are aligned in adirection perpendicular to a surface of the film. In FIG. 3, (1)corresponds to the indium zinc oxide film in FIG. 2A, and (2)corresponds to the indium zinc oxide film in FIG. 2B. For themeasurement apparatus and the measurement method, Embodiment 1 can bereferred to.

In FIG. 3, (1) represents the XRD data of the indium zinc oxide filmformed in the following manner: a silicon oxynitride film was formed asa base film over a substrate, and then the indium zinc oxide film isformed over the base film of the silicon oxynitride film. In addition,(2) in FIG. 3 represents the XRD data of the indium zinc oxide filmformed in the following manner: a silicon oxide film is formed as a basefilm over a substrate, and then the indium zinc oxide film is formedover the base film of the silicon oxide film.

In FIG. 3, the diffraction peaks obtained by XRD measurement are in thevicinity of 31°.

It can be found from the measurement results of the cross-sectional TEMphotographs in FIGS. 2A and 2B and the measurement results of the XRDdata in FIG. 3 that the indium zinc oxide films formed by a sputteringmethod under conditions of the substrate temperature of 200° C. orhigher include CAAC parts.

The comparison between FIGS. 1A and 1B and FIGS. 3A and 3B reveals thefact that as the amount of an oxygen gas added in film formation islarger, the indium zinc oxide film is likely to include more CAAC parts.

Next, measurement results of XRD data are shown in FIG. 4.

The film formation conditions of the indium zinc oxide films shown inFIG. 4 are as follows: the composition of the target is In:Zn=2:1, thegas ratio is an argon gas:an oxygen gas=7:3, the substrate temperatureis 25° C. (room temperature), the reaction pressure is 0.4 Pa, and theDC power is 0.5 kW.

Note that the nitrogen annealing treatment was not performed on theseindium zinc oxide films after the film formation.

In FIG. 4, (1) represents the XRD data of the indium zinc oxide filmformed in the following manner: a silicon oxynitride film was formed asa base film over a substrate, and then the indium zinc oxide film isformed over the base film of the silicon oxynitride film. In addition,(2) in FIG. 4 represents the XRD data of the indium zinc oxide filmformed in the following manner: a silicon oxide film is formed as a basefilm over a substrate, and then the indium zinc oxide film is formedover the base film of the silicon oxide film.

As is apparent from FIG. 4, diffraction peaks were not substantiallyobserved in the vicinity of 31° in the indium zinc oxide films after thefilm formation by XRD measurement. As compared with FIG. 3, thedifference of the diffraction peaks in the vicinity of 31° is obvious.Consequently, the indium zinc oxide films obtained under theabove-described film formation conditions are indium zinc oxide filmshaving an amorphous structure.

From the comparison between XRD data in FIG. 3 and that in FIG. 4, itcan be found that in the case where the amount of an oxygen gas added infilm formation is small and the substrate temperature is low(approximately room temperature), the indium zinc oxide film does notinclude CAAC parts and has an amorphous structure.

From the comparison between XRD data in FIGS. 1A and 1B and that in FIG.3, it can be found that when the amount of an oxygen gas in filmformation is small, the indium zinc oxide film is unlikely to includeCAAC parts.

Next, FIGS. 5A and 5B and FIG. 11 show measurement results of XRD dataof indium zinc oxide films formed by a sputtering method in anatmosphere including an argon gas under conditions of the substratetemperature of higher than or equal to 200° C. and then subjected tonitrogen annealing treatment.

Film formation conditions of the indium zinc oxide films shown in FIGS.5A and 5B are as follows: the composition of the target is In:Zn=2:1,the gas ratio is an argon gas:an oxygen gas=7:3, the substratetemperature is 200° C., the reaction pressure is 0.4 Pa, and the DCpower is 0.5 kW.

FIG. 5A shows the measurement results of the XRD data in the case wherethe temperature of the nitrogen annealing treatment is 350° C. and thetime of the nitrogen annealing treatment is 1 hour. FIG. 5B shows themeasurement results of the XRD data in the case where the temperature ofthe nitrogen annealing treatment is 450° C. and the time of the nitrogenannealing treatment is 1 hour.

The film formation conditions of the indium zinc oxide films shown inFIG. 11 are as follows: the composition of the target is In:Zn=2:1, thepercentage of an oxygen gas in film formation is 100%, the substratetemperature is 200° C., the reaction pressure is 0.4 Pa, and the DCpower is 0.5 kW. FIG. 11 shows the measurement results of the XRD datain the case where the temperature of the nitrogen annealing treatment is350° C. and the time of the nitrogen annealing treatment is 1 hour.

For the measurement apparatus and the measurement method, Embodiment 1can be referred to.

In FIGS. 5A and 5B and FIG. 11, (1) represents the XRD data of theindium zinc oxide film formed over a base film of a silicon oxynitridefilm.

In FIGS. 5A and 5B and FIG. 11, (2) represents the XRD data of theindium zinc oxide film formed over the base film of the silicon oxidefilm.

In FIGS. 5A and 5B, the diffraction peaks obtained by XRD measurementare in the vicinity of 31°.

These results show that even if nitrogen annealing treatment isperformed on an indium zinc oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film, the crystal structure in which c-axes are aligned in adirection perpendicular to a surface of the film is maintained.

Next, the measured sheet resistances of the indium zinc oxide films usedin FIGS. 5A and 5B are shown in Table 2 and Table 3. The sheetresistance of the indium zinc oxide film on which nitrogen annealingtreatment is performed at a treatment temperature of 350° C. for 1 hourand the sheet resistance of the indium zinc oxide film on which nitrogenannealing treatment is performed at a treatment temperature of 450° C.for 1 hour are compared.

TABLE 2 Indium zinc oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmArgon:Oxygen 70%:30% Substrate temperature 200° C. Nitrogen annealingtreatment Performed at 350° C. Base film Silicon oxide film Sheetresistance [Ω/□] 2830

TABLE 3 Indium zinc oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmArgon:Oxygen 70%:30% Substrate temperature 200° C. Nitrogen annealingtreatment Performed at 450° C. Base film Silicon oxide film Sheetresistance [Ω/□] 2300

For the measurement apparatus and the measurement method, Embodiment 1can be referred to.

The indium zinc oxide film shown in Table 2 corresponds to the indiumzinc oxide film having the XRD data of (2) in FIG. 5A.

The indium zinc oxide film shown in Table 3 corresponds to the indiumzinc oxide film having the XRD data of (2) in FIG. 5B.

The sheet resistance in the case where the nitrogen annealing treatmenttemperature is 350° C. is approximately 2830 Ω/□, while the sheetresistance in the case where the nitrogen annealing treatmenttemperature is 450° C. is approximately 2300 Ω/□ This shows that highernitrogen annealing treatment temperature causes lower sheet resistance.

Accordingly, higher nitrogen annealing treatment temperature offers anindium zinc oxide film with higher conductivity.

Next, the measured sheet resistances of the indium zinc oxide films usedin FIG. 4 and FIG. 11 are shown in Table 4 and Table 5.

The indium zinc oxide film having an amorphous structure shown in Table4 corresponds to the indium zinc oxide film having the XRD data of (2)in FIG. 4. The indium zinc oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film shown in Table 4 corresponds to the indium zinc oxide filmhaving the XRD data of (2) in FIG. 11.

TABLE 4 Indium zinc oxide film having a crystal structure in whichc-axes are aligned in a Indium zinc oxide film direction perpendicularhaving an amorphous to a surface of the film structure Argon:Oxygen0%:100% 70%:30% Substrate temperature 200° C. Room temperature Nitrogenannealing Performed at 350° C. Not performed treatment Base film Siliconoxide film Silicon oxide film Sheet resistance [Ω/□] 1270 5M or higherThickness [nm] 100.89 99.20

The indium zinc oxide film having an amorphous structure shown in Table5 corresponds to the indium zinc oxide film having the XRD data of (1)in FIG. 4. The indium zinc oxide film having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film shown in Table 5 corresponds to the indium zinc oxide filmhaving the XRD data of (1) in FIG. 11.

TABLE 5 Indium zinc oxide film having a crystal structure in whichc-axes are aligned in a Indium zinc oxide film direction perpendicularhaving an amorphous to a surface of the film structure Argon:Oxygen0%:100% 70%:30% Substrate temperature 200° C. Room temperature Nitrogenannealing Performed at 350° C. Not performed treatment Base film Siliconoxynitride film Silicon oxynitride film Sheet resistance [Ω/□] 1100 5Mor higher Thickness [nm] 100.07 99.34

As shown in Table 4 and Table 5, the sheet resistances of the indiumzinc oxide films having a crystal structure in which c-axes are alignedin a direction perpendicular to a surface of the films are approximately1000 Ω/□, while the sheet resistances of the indium zinc oxide filmshaving an amorphous structure are 5M θ/□ or higher. In other words, thesheet resistances of the indium zinc oxide films having a crystalstructure in which c-axes are aligned in a direction perpendicular to asurface of the films are by three orders of magnitude lower than thoseof the indium zinc oxide films having an amorphous structure.

Thus, the indium zinc oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmhas higher conductivity than the indium zinc oxide film having anamorphous structure.

Next, the measured band gaps of the indium zinc oxide films used in FIG.3, FIG. 4, and FIG. 11 are shown in Table 6 and Table 7.

TABLE 6 Indium zinc oxide film having a Indium zinc oxide crystalstructure in which c-axes are film having an aligned in a directionperpendicular to amorphous a surface of the film structure Argon:Oxygen0%:100% 0%:100% 70%:30% Substrate 200° C. 200° C. Room temperaturetemperature Nitrogen Not performed Performed Not performed annealingtreatment at 350° C. Base film Silicon oxide film Silicon oxide filmSilicon oxide film Band gap [eV] 2.56 2.61 2.52 Thickness [nm] 99.40100.89 99.20

TABLE 7 Indium zinc oxide film having a Indium zinc oxide crystalstructure in which c-axes are film having an aligned in a directionperpendicular to amorphous a surface of the film structure Argon:Oxygen0%:100% 0%:100% 70%:30% Substrate 200° C. 200° C. Room temperaturetemperature Nitrogen Not performed Performed Not performed annealingtreatment at 350° C. Base film Silicon oxynitride Silicon oxynitrideSilicon oxynitride film film film Band gap [eV] 2.53 2.62 2.45 Thickness[nm] 99.92 100.07 99.34

The indium zinc oxide film having an amorphous structure shown in Table6 corresponds to the indium zinc oxide film having the XRD data of (2)in FIG. 4. The indium zinc oxide film having an amorphous structureshown in Table 7 corresponds to the indium zinc oxide film having theXRD data of (1) in FIG. 4.

The band gap of the indium zinc oxide film having an amorphous structureformed over the base film of the silicon oxide film, which correspondsto (2) in FIG. 4, is 2.52 eV.

The band gap of the indium zinc oxide film having an amorphous structureformed over the base film of the silicon oxynitride film, whichcorresponds to (1) in FIG. 4, is 2.45 eV.

The indium zinc oxide films having a crystal structure in which c-axesare aligned in a direction perpendicular to a surface of the film shownin Table 6 correspond to the indium zinc oxide film having the XRD dataof (2) in FIG. 3 and the indium zinc oxide film having the XRD data of(2) in FIG. 11. The indium zinc oxide films having a crystal structurein which c-axes are aligned in a direction perpendicular to a surface ofthe film shown in Table 7 correspond to the indium zinc oxide filmhaving the XRD data of (1) in FIG. 3 and the indium zinc oxide filmhaving the XRD data of (1) in FIG. 11.

The band gap of the CAAC indium zinc oxide film formed over the basefilm of the silicon oxide film, which corresponds to (2) in FIG. 3, is2.56 eV. The band gap of the CAAC indium zinc oxide film formed over thebase film of the silicon oxide film, which corresponds to (2) in FIG.11, is 2.61 eV.

The band gaps of the indium zinc oxide films having a crystal structurein which c-axes are aligned in a direction perpendicular to a surface ofthe films is larger by about 0.05 eV than that of the indium zinc oxidefilm having an amorphous structure.

The band gap of the CAAC indium zinc oxide film formed over the basefilm of the silicon oxynitride film, which corresponds to (1) in FIG. 3,is 2.53 eV. The band gap of the CAAC indium zinc oxide film formed overthe base film of the silicon oxynitride film, which corresponds to (1)in FIG. 11, is 2.62 eV.

The band gaps of the indium zinc oxide films having a crystal structurein which c-axes are aligned in a direction perpendicular to a surface ofthe films is larger by about 0.1 eV than that of the indium zinc oxidefilm having an amorphous structure.

From the measurement results in Table 6 and Table 7, it can be foundthat the band gaps of the indium zinc oxide films having a crystalstructure in which c-axes are aligned in a direction perpendicular to asurface of the films were larger than those of the indium zinc oxidefilms having an amorphous structure.

Further, as shown in Table 6 and Table 7, the band gaps of the indiumzinc oxide films that have a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the films and aresubjected to nitrogen annealing treatment at 350° C. after the filmformation is larger than that of the indium zinc oxide films that have acrystal structure in which c-axes are aligned in a directionperpendicular to a surface of the films and are not subjected tonitrogen annealing treatment after the film formation.

Thus, the indium zinc oxide films having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmhave higher light transmittance than the indium zinc oxide film havingan amorphous structure.

Further, the indium zinc oxide film subjected to nitrogen annealingtreatment has higher light transmittance than the indium zinc oxide filmnot subjected to nitrogen annealing treatment. Consequently, it issuggested that the nitrogen annealing treatment is efficient forincreasing not only the conductivity of the indium zinc oxide film butalso the light transmittance thereof.

This embodiment can be implemented in appropriate combination with anyof the other embodiments described in this specification.

Embodiment 3

In this embodiment, an example of using the conductive oxide film of oneembodiment of the present invention in an organic EL display devicehaving a touch panel is described with reference to FIGS. 6A and 6B andFIGS. 7A and 7B.

As an example, an analog resistive touch panel is described withreference to FIGS. 6A and 6B.

FIG. 6A is a cross-sectional view of an organic EL display device 100having a touch panel 20, and FIG. 6B illustrates the placement ofconductive oxide films in the touch panel 20.

The organic EL display device 100 includes an organic EL display panel10 and a touch panel 20. Although the organic EL display panel 10 andthe touch panel 20 are directly bonded with an adhesive layer 300provided therebetween in FIG. 6A, another structure may be employed.Part of the organic EL display panel 10 may be bonded to part of thetouch panel 20 with an adhesive layer.

As illustrated in FIG. 6A, the touch panel 20 includes a first substrate200, a second substrate 210, a first conductive oxide film 201, a secondconductive oxide film 202, a dot spacer 203, a sealant 204, and an airgap 205.

Further, as illustrated in FIG. 6A, the organic EL display panel 10includes a first substrate 110, a base layer 101 over the firstsubstrate 110, a transistor 102 and an insulating layer 103 over thebase layer 101, a first interlayer film 104 over the insulating layer103, a wiring 105 electrically connected to the transistor 102, a secondinterlayer film 106 over the wiring 105 and the first interlayer film104, a light-emitting element 107 electrically connected to the wiring105, and a first partition 114 and a second partition 155 which isolatethe light-emitting element 107. In addition, a second substrate 160 isincluded as an opposite substrate of the first substrate 110. The secondsubstrate 160 is provided with a base layer 162, a black matrix 163, ared color filter 164, a green color filter 165, and a blue color filter166. The light-emitting element 107 includes a reflective electrode 108,a first microcavity layer 109, a second microcavity layer 111, alight-emitting layer 112, and a cathode 113.

As materials of the first conductive oxide film 201 and the secondconductive oxide film 202, an indium zinc oxide is particularlypreferably used.

Note that the conductive oxide films having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of thefilm, described in Embodiments 1 and 2, can be used as the firstconductive oxide film 201, the second conductive oxide film 202, thecathode 13, the first microcavity layer 109, and the second microcavitylayer 111. The conductive oxide films have high conductivity and hightransmittance of visible light.

As a material that can be used as the dot spacer 203, alight-transmitting elastic material is preferably used; an insulatingsynthetic resin such as an epoxy resin or an acrylic resin is preferablyused. The dot spacer 203 may contain a microparticle of an organicsubstance, silicon (Si), carbon (C), magnesium (Mg), or the like.

The dot spacer 203 can reduce impact between the first substrate 200 andthe second substrate 210 given when an input means 115 touches the touchpanel 20. In addition, the dot spacer 203 makes it easy for the firstsubstrate 200 to return to the original position after the input means115 touches the touch panel 20.

The dot spacer 203 may be formed on either the second substrate 210 sideor the first substrate 200 side. Alternatively, the dot spacer 203 maybe formed on both the first substrate 200 side and the second substrate210 side.

As examples of materials that can be used as the first substrate 200 andthe second substrate 210, a plastic film, glass, thin plate glass,reinforced glass, and the like can be given. The plastic film is notparticularly limited but preferably one having a light-transmittingproperty and an upper temperature limit of 200° C. or higher. As theplastic film, polyethylene terephthalate (PET, upper temperature limit:approximately 200° C.), polyethylene naphthalate (PEN, upper temperaturelimit: approximately 200° C.), polyether sulfone (PES, upper temperaturelimit: approximately 200° C.), cyclic olefin copolymer (COC, uppertemperature limit: approximately 200° C.), triacetylcellulose (TAC,upper temperature limit: approximately 200° C.), polyimide (PI, uppertemperature limit: approximately 200° C.), polyester (upper temperaturelimit: approximately 240° C.), a silicone resin (upper temperaturelimit: approximately 500° C.), or the like is preferably used.

Alternatively, a plastic film having an upper temperature limit of 200°C. or lower can also be used. Preferred examples of the plastic filmhaving an upper temperature limit of 200° C. or lower include polyvinylalcohol (PVA, upper temperature limit: approximately 40° C. to 60° C.),polystyrene (PS, upper temperature limit: approximately 70° C. to 90°C.), biaxially oriented polystyrene sheet (OPS, upper temperature limit:approximately 80° C.), polyvinyl chloride (PVC, upper temperature limit:approximately 60° C. to 80° C.), polycarbonate (PC, upper temperaturelimit: approximately 120° C. to 130° C.), polymethylmethacrylate (PMMA,upper temperature limit: approximately 70° C. to 90° C.), and the like.

In the case of using the plastic film having an upper temperature limitof 200° C. or lower, a base film is preferably formed between theconductive oxide film and the substrate. As the base film, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, or thelike can be used. By forming the base film between the conductive oxidefilm and the substrate, the influence of gas generated from the plasticfilm or the like can be reduced. In addition, defects in the crystal ofthe conductive oxide film can be reduced.

A preferred material that can be used as the sealant 204 includes butnot limited to a double adhesive tape (DAT) or the like.

The sealant 204 is provided on an edge portion of one surface of thefirst substrate 200 and an edge portion of one surface of the secondsubstrate 210. The edge portions of the first substrate 200 and thesecond substrate 210 are bonded to each other. The sealant 204 separatesthe first conductive oxide film 201 from the second conductive oxidefilm 202 during the time when the input means 115 does not touch thetouch panel 20.

As illustrated in FIG. 6B, the first conductive oxide film 201 is formedevenly on a surface of the first substrate 200. The second conductiveoxide film 202 is formed evenly on a surface of the second substrate210.

A method for sensing the touch position in the touch panel 20 isdescribed. In the case of an analog resistive type, voltage is appliedto one of the first conductive oxide film 201 and the second conductiveoxide film 202, and a potential is detected from the other of theconductive oxide films. When the input means 115 touches a surface ofthe first substrate 200 in the state where the air gap 205 and the dotspacer 203 separate the first conductive oxide film 201 from the secondconductive oxide film 202, the first conductive oxide film 201 bends inthe direction of the second conductive oxide film 202, and the firstconductive oxide film 201 contacts with the second conductive oxide film202. At this time, the first conductive oxide film 201 and the secondconductive oxide film 202 are brought into conduction. By detecting thepotential of the conducting point, the touch position can be sensed.Note that since the conductive oxide films have high conductivity andhigh transmittance of visible light, the sensing accuracy of the touchposition in the touch panel 20 can be increased.

For example, in the case where the touch panel 20 is a 4-wire panel,electrodes (not necessarily transparent) are provided in four locations:over and under the first conductive oxide film 201 and on sides of thesecond conductive oxide film 202. Then, voltage is applied to only oneof the conductive oxide films, and the potential of the touch positionis detected from the other conductive oxide film; thus, the touchposition can be sensed. The touch panel 20 may be a 5-wire, 7-wire, or8-wire panel, without being limited to a 4-wire panel.

Alternatively, the touch panel 20 may be a surface capacitive touchpanel 40 as illustrated in FIGS. 7A and 7B.

An example of using the touch panel 40 in an organic EL display deviceis described with reference to FIGS. 7A and 7B.

FIG. 7A is a cross-sectional view of an organic EL display device 440having the touch panel 40, and FIG. 7B illustrates the placement ofconductive oxide films in the touch panel 40.

As illustrated in FIG. 7A, the touch panel 40 includes a first substrate400, a conductive oxide film 401, and a second substrate 402.

As a material of the conductive oxide film 401, an indium zinc oxide isparticularly preferably used.

Any of the conductive oxide films having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of thefilm, described in Embodiments 1 and 2, can be used as the conductiveoxide film 401. The conductive oxide films have high conductivity andhigh transmittance of visible light. Accordingly, the sensing accuracyof the touch position in the touch panel 40 can be increased.

Any of the materials similar to those of the touch panel 20 can be usedas the first substrate 400 and the second substrate 402.

In the organic EL display device 440 illustrated in FIG. 7A, part of theorganic EL display panel 10 is bonded to part of the touch panel 40 withan adhesive layer 403. Although a space is formed in the non-bondedarea, the conductive oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmcan prevent a reduction in light transmittance.

As illustrated in FIG. 7B, the conductive oxide film 401 is formedevenly on a surface of the second substrate 402.

A method for sensing the touch position in the touch panel 40 isdescribed. Electrodes (not necessarily transparent) are provided at fourcorners of the conductive oxide film 401. Since the conductive oxidefilm 401 is formed evenly on the surface of the second substrate 402,when voltage is applied to these four electrodes, an electric field isevenly generated in the touch panel 40. At this time, little currentflows in the conductive oxide film 401.

When the input means 215 touches a surface of the first substrate 400, acurrent flowing through the conductive oxide film 401 is changed (a weakelectric current flows). Since capacitance is generated between theinput means 215 and the conductive oxide film 401 at this time,capacitance (total capacitance) of the touch panel 40 is increased, sothat the amount of current flowing in the electrodes at four corners ofthe conductive oxide film 401 changes. Since a closed circuit is formedof the conductive oxide film 401, the first substrate 400, the inputmeans 215, and GND, the current flowing through the electrodes at fourcorners is sensed, and the touch position can be precisely obtained fromthe ratio of the distances between the touch position and the electrodesat four corners.

Note that in the capacitive touch panel 40, the touch position can besensed even when the input means 215 does not directly touch the firstsubstrate 400 but only comes close to the first substrate 400.

Although the case of using an analog resistive touch panel as the touchpanel 20 and a surface capacitive touch panel as the touch panel 40 havebeen described in this embodiment, the structure of the touch panel 20and the touch panel 40 are not limited to these structures. In eithercase, any of the conductive oxide films having a crystal structure inwhich c-axes are aligned in a direction perpendicular to a surface ofthe film, described in Embodiments 1 and 2, can be used as theconductive oxide film in the touch panel.

The structures of the out-cell organic EL display devices in which thetouch panel 20 or the touch panel 40 is externally attached to theorganic EL display panel 10 have been described in this embodiment;however, the structure is not limited to the out-cell structure. Anin-cell or on-cell organic EL display device having a touch panelfunction similar to that of the touch panel 20 or the touch panel 40 maybe formed.

In the case where the touch panel function similar to that of the touchpanel 20 or the touch panel 40 is provided inside an organic EL displaydevice, the conductive oxide film serves as a touch electrode (sensorelectrode). By forming an anode (or a cathode) and a conductive oxidefilm over the same substrate, the control of a light-emitting layer fordisplaying images on the organic EL display device and the sensing ofthe touch position of the input means on the display panel can beconducted over the same substrate. The conductive oxide film can serveas both the touch electrode and the electrode for controlling thelight-emitting layer. Thus, when a touch panel function is providedinside an organic EL display device, there is no need to additionallyprovide a touch panel over the organic EL display panel; accordingly,the thickness of the whole organic EL display device can be reduced andfurther the weight of the whole organic EL display device can bereduced.

By using the conductive oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmand having high conductivity and high transmittance of visible light ina touch panel and an organic EL display panel, the organic EL displaydevice can have high performance.

This embodiment can be implemented in appropriate combination with anyof the other embodiments described in this specification.

Embodiment 4

In this embodiment, electronic devices having a touch panel capable ofmulti-touch input are described with reference to FIGS. 8A to 8C, FIGS.9A to 9C, and FIGS. 10A to 10C. Examples of electronic devices include aportable television device (also referred to as a television or atelevision receiver), a camera such as a digital camera or a digitalvideo camera, a digital photo frame, a mobile phone, a portable gamemachine, a portable information terminal, an audio reproducing device, agame machine (such as a pachinko machine or a slot machine), a gameconsole, and the like. Any of the conductive oxide films having acrystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film, described in Embodiments 1 and2, can be used in these electronic devices.

Display panels incorporated in these electronic devices may be liquidcrystal display panels or organic EL display panels.

FIGS. 8A to 8C illustrate a specific example of an electronic device9600. FIGS. 8A and 8B illustrate a foldable tablet terminal. The tabletterminal includes a CPU and the like to which power supply voltage issupplied from a battery.

FIG. 8A illustrates an opened state, and FIG. 8B illustrates a closedstate.

As illustrated in FIG. 8A, the tablet terminal includes a housing 9630,a display portion 9631 a, a display portion 9631 b, a display modeswitch 9034, a power switch 9035, a power saver switch 9036, a clasp9033, and an operation switch 9638.

Part or the whole of the display portion 9631 a can be a touch panelregion 9632 a. Multi-touch input is possible in the touch panel region9632 a. When a user touches a plurality of operation keys 9640 displayedon the display portion 9631 a at a time with fingers or the like toinput data, a plurality of touch positions can be sensed precisely.

A touch panel 9800 a illustrated in FIG. 9A is provided in the displayportion 9631 a.

In the display portion 9631 b, part or the whole of the display portion9631 b can be a touch panel region 9632 b, in a manner similar to thatof the display portion 9631 a. By touching a keyboard display switchingbutton 9639 displayed on the display portion 9631 b with a finger, astylus pen, or the like, keyboard buttons can appear on the displayportion 9631 b. Multi-touch input is possible in the touch panel region9632 b. When a user touches a plurality of operation keys 9637 displayedon the display portion 9631 b at a time with fingers, stylus pens, orthe like, a plurality of touch positions can be sensed precisely.

A touch panel 9800 b illustrated in FIG. 10A is provided in the displayportion 9631 b.

Touch input can be performed in the touch panel region 9632 a and thetouch panel region 9632 b at a time.

Note that FIG. 8A shows, as an example, that half of the area of thedisplay portion 9631 a has only a display function, and the other halfof the area has a touch panel function; however, the present inventionis not limited to this structure. Keyboard buttons can be displayed onthe entire screen of the display portion 9631 a so that the entirescreen of the display portion 9631 a is used as a touch panel region,whereas the display portion 9631 b can be used as a display screen.

The display mode switch 9034 can switch the display between a portraitmode, a landscape mode, and the like, and between monochrome display andcolor display, for example. The power saver switch 9036 can optimizedisplay luminance in accordance with the amount of external lightdetected by an optical sensor incorporated in the tablet terminal whenthe tablet terminal is in use. In addition to the optical sensor,another detection device including a sensor for detecting inclination,such as a gyroscope sensor or an acceleration sensor, may beincorporated in the tablet terminal. Note that in the power-saving mode,supply of power supply voltage to the CPU included in the tabletterminal may be completely stopped.

Although the display portion 9631 a and the display portion 9631 b havethe same display area in FIG. 8A, one embodiment of the presentinvention is not limited to this example. They may differ in size and/orimage quality. For example, higher definition images may be displayed onone of the display portions 9631 a and 9631 b.

FIG. 9A is a cross-sectional view of the touch panel 9800 a. FIGS. 9Band 9C illustrate the placement of conductive oxide films. In FIG. 9A,an example of using a projected capacitive (mutual capacitive) touchpanel as the touch panel 9800 a is illustrated. A chain line A-A′ inFIG. 9A corresponds to those in FIGS. 9B and 9C. By employing any of theconductive oxide films having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film, describedin Embodiments 1 and 2, in the touch panel 9800 a, the sensing accuracyof the touch panel 9800 a can be increased.

As illustrated in FIG. 9A, the touch panel 9800 a includes a firstsubstrate 500, a second substrate 510, first conductive oxide films 501,second conductive oxide films 502, and an insulating layer 503.

As materials of the first conductive oxide films 501 and the secondconductive oxide films 502, an indium zinc oxide is particularlypreferably used.

Note that the first conductive oxide films 501 and the second conductiveoxide films 502 each having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film have highconductivity and high transmittance of visible light.

As illustrated in FIG. 9C, the plurality of first conductive oxide films501 each having a shape of rhombuses linking together in thelongitudinal direction are formed over the first substrate 500. Asillustrated in FIG. 9B, the plurality of second conductive oxide films502 each having a shape of rhombuses linking together in the lateraldirection are formed over the second substrate 510. Alternatively, theplurality of first conductive oxide films 501 may also be arranged inthe lateral direction, and the plurality of second conductive oxidefilms 502 may also be arranged in the longitudinal direction.

Alternatively, the plurality of first conductive oxide films 501 may bearranged in an oblique direction, and the plurality of second conductiveoxide films 502 may be arranged in an oblique direction that isdifferent from the oblique direction of the first conductive oxide films501. In any case, the first conductive oxide films 501 and the secondconductive oxide films 502 are arranged so as to produce overlappingportions of the first conductive oxide films 501 and the secondconductive oxide films 502.

The shapes of the first conductive oxide films 501 and the secondconductive oxide films 502 are not limited to the shapes illustrated inFIGS. 9A to 9C. The shape may be the shape of a stripe, a quadrangle,the shape of hexagons linking together, or the shape of alternatelyconnecting a triangle and a rhombus.

A method for sensing the touch position in the touch panel 9800 a isdescribed. In the overlapping portions of the first conductive oxidefilms 501 and the second conductive oxide films 502, mutual capacitanceis generated between the first conductive oxide films 501 and the secondconductive oxide films 502. In the mutual capacitive touch panel 9800 a,the mutual capacitance is utilized to sense the touch position. Themutual capacitance is changed by the touch of the touch panel 9800 awith the input means 515, and the touch position is sensed by sensingthe change.

Note that in a self-capacitance touch panel, the touch position issensed utilizing self-capacitance (the capacitance generated between theinput means 515 and the first conductive oxide film 501, and thecapacitance generated between the input means 515 and the secondconductive oxide film 502). The self-capacitance is changed by the touchof the touch panel with the input means, and the touch position issensed by the change. In this embodiment, an example of using aprojected-capacitive touch panel of a mutual-capacitive type as thetouch panel 9800 a is described; however, a projected-capacitive touchpanel of a self-capacitive type may be used as any one of the touchpanels that do not require a multi-touch sensing function among thetouch panels described in this specification. The self-capacitance touchpanel can more easily reduce power consumption than the mutualcapacitive touch panel.

In the mutual capacitive touch panel 9800 a, either the first conductiveoxide films 501 or the second conductive oxide films 502 serve asdriving electrodes, and the other conductive oxide films serve asreception electrodes. For example, in the case where the firstconductive oxide films 501 serve as driving electrodes, driving voltageis sequentially applied to the plurality of electrodes (the firstconductive oxide films 501). When the input means 515 touches the touchpanel 9800 a, the mutual capacitance between the first conductive oxidefilm 501 and the second conductive oxide film 502 is changed. The changein mutual capacitance changes the potential of the electrodecorresponding to the touch position. In the mutual capacitive touchpanel 9800 a, by sequentially detecting potentials of the plurality ofelectrodes (the second conductive oxide films 502) serving as receptionelectrodes, the position where the change in potential (mutualcapacitance) occurs is selectively sensed, so that the touch positioncan be sensed. Since the touch position can be selectively andsequentially sensed in the mutual capacitive touch panel, multi-touch ispossible unlike the self-capacitance touch panel. In theself-capacitance touch panel, the way of sensing the potential change(self-capacitance change) using all of a plurality of electrodes (e.g.,a plurality of conductive oxide films arranged in the longitudinaldirection or a plurality of conductive oxide films arranged in thelateral direction) is conducted. Consequently, when the input means 515touches a plurality of points on a surface of the first substrate 500 ata time, the touch positions can be sensed precisely.

FIG. 10A is a cross-sectional view of the touch panel 9800 b. FIGS. 10Band 10C illustrate the placement of conductive oxide films. In FIG. 10A,an example of using a digital resistive touch panel as the touch panel9800 b is illustrated. A chain line B-B′ in FIG. 10A corresponds to thatin FIGS. 10B and 10C. By employing any of the conductive oxide filmshaving a crystal structure in which c-axes are aligned in a directionperpendicular to a surface of the film, described in Embodiments 1 and2, in the touch panel 9800 b, the sensing accuracy of the touch panel9800 b can be increased. Note that a resistive touch panel has anadvantage of easy input with a pen.

As illustrated in FIG. 10A, the touch panel 9800 b includes a firstsubstrate 600, a second substrate 610, first conductive oxide films 601,second conductive oxide films 602, a dot spacer 603, a sealant 604, andan air gap 605. Embodiment 3 can be referred to for the detaileddescription of the structure.

As materials of the first conductive oxide film 601 and the secondconductive oxide film 602, an indium zinc oxide is particularlypreferably used.

Note that the first conductive oxide films 601 and the second conductiveoxide films 602 each having a crystal structure in which c-axes arealigned in a direction perpendicular to a surface of the film have highconductivity and high transmittance of visible light.

As illustrated in FIG. 10C, the plurality of first conductive oxidefilms 601 each having the shape of a stripe or a quadrangle in thelongitudinal direction are formed over the first substrate 600. Asillustrated in FIG. 10B, the plurality of second conductive oxide films602 each having the shape of a stripe or a quadrangle in the lateraldirection are formed over the second substrate 610. Alternatively, theplurality of first conductive oxide films 601 may also be arranged inthe lateral direction, and the plurality of second conductive oxidefilms 602 may also be arranged in the longitudinal direction.

The shapes of the first conductive oxide films 601 and the secondconductive oxide films 602 are not limited to the shapes illustrated inFIGS. 10A to 10C. The shape may be the shape of hexagons linkingtogether or the shape of alternately connecting a triangle and arhombus. In the digital resistive touch panel, the first conductiveoxide films 601 and the second conductive oxide films 602 are not evenlyformed over the substrate surface and are formed so as to be isolatedfrom each other unlike the analog resistive touch panel. Since theelectrodes are independently formed, multi-touch is possible.

A method for sensing the touch position in the touch panel 9800 b isdescribed. When an input means 615 touches a surface of the firstsubstrate 600 in the state where the air gap 605 and the dot spacer 603isolate the first conductive oxide films 601 from the second conductiveoxide films 602, the first conductive oxide film 601 bends in thedirection of the second conductive oxide film 602, and the firstconductive oxide film 601 and the second conductive oxide film 602contact with each other and are brought into conduction. At this time,since the first conductive oxide films 601 and the second conductiveoxide films 602 have their own independent electrodes, the potentials ofa plurality of touch positions can be detected. Thus, the touchpositions can be sensed precisely.

For example, in the case of the touch panel 9800 b, driving voltage isapplied to a plurality of upper electrodes (the first conductive oxidefilms 601) to sequentially drive the upper electrodes, and the potentialof the touch position is detected from the lower electrode (the secondconductive oxide film 602) during the driving period; thus, the touchposition can be sensed. Alternatively, the touch position can be sensedin the following manner: driving voltage is applied to a plurality oflower electrodes to sequentially drive the lower electrodes, and thepotential of the touch position is detected from the upper electrodeduring the driving period. Further alternatively, the touch position canbe sensed in the following manner: driving voltage is sequentiallyapplied to the plurality of upper electrodes and then driving voltage issequentially applied to the plurality of lower electrodes (drivingvoltage is applied alternately to the upper electrodes and the lowerelectrodes), and the potential of the touch position is detected fromthe electrode to which driving voltage is not applied. By using anappropriate sensing method, a plurality of touch positions can be sensedprecisely. The driving method for sensing the touch position in thedigital resistive touch panel 9800 b is not particularly limited.

Note that since the first conductive oxide films 601 and the secondconductive oxide films 602 have high conductivity and high transmittanceof visible light, the sensing accuracy of the touch position in thetouch panel 9800 b can be increased.

The above-described touch panel 9800 (the touch panel 9800 a and thetouch panel 9800 b) can be externally provided outside a display panel;thus, the electronic device 9600 having the out-cell display panelillustrated in FIG. 8A can be formed.

Alternatively, the touch panel 9800 can be freely incorporated in thedisplay panel in the display portion 9631. The electronic device 9600including an in-cell display panel having a touch panel function similarto that of the touch panel 9800 may be formed. The electronic device9600 including an on-cell display panel having a touch panel functionsimilar to that of the touch panel 9800 may be formed.

For example, a touch panel function similar to that of the touch panel9800 may be incorporated in a pixel of a liquid crystal display device.In this case, the first conductive oxide films and the second conductiveoxide films have a function of a touch electrode, and a liquid crystallayer is sandwiched between the first conductive oxide films and thesecond conductive oxide films. The first conductive oxide films (secondconductive oxide films) may be provided separate from a pixel electrodeand a common electrode so as to have only a function of a touchelectrode. Alternatively, the first conductive oxide films (secondconductive oxide films) may be provided separate from a pixel electrodeso as to have both a function of a touch electrode and a function of apixel electrode. Further alternatively, the first conductive oxide films(second conductive oxide films) may be provided separate from a commonelectrode so as to have both a function of a touch electrode and afunction of a pixel electrode.

For example, a touch panel function similar to that of the touch panel9800 may be incorporated in a pixel of an organic EL display device. Inthis case, the first conductive oxide films and the second conductiveoxide films have a function of a touch electrode, and a light-emittinglayer is sandwiched between the first conductive oxide films and thesecond conductive oxide films. The first conductive oxide films (secondconductive oxide films) may be provided separate from a cathode and ananode so as to have only a function of a touch electrode. Alternatively,the first conductive oxide films (second conductive oxide films) may beprovided separate from a cathode so as to have both a function of atouch electrode and a function of an anode. Further alternatively, thefirst conductive oxide films (second conductive oxide films) may beprovided separate from an anode so as to have both a function of a touchelectrode and a function of a cathode.

For example, in a liquid crystal display device or an organic EL displaydevice, the first conductive oxide films are formed over a surface of asubstrate opposite to the surface on which a color filter is formed, andthe second conductive oxide films are formed over a surface of asubstrate opposite to the surface on which a polarizing plate is formed;thus, a touch panel function similar to that of the touch panel 9800 canbe incorporated in the liquid crystal display device or the organic ELdisplay device.

Next, the tablet terminal in the closed state is described.

As illustrated in FIG. 8B, the tablet terminal includes the housing9630, a solar cell 9633, a charge/discharge control circuit 9634, abattery 9635, and a DC-DC converter 9636. Note that FIG. 8B illustratesan example in which the charge/discharge control circuit 9634 has thebattery 9635 and the DCDC converter 9636.

Any of the conductive oxide films having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of thefilm, described in Embodiments 1 and 2, can be used in the solar cell9633. Since the conductive oxide film has high conductivity and hightransmittance of visible light, the solar cell 9633 can have highperformance.

Since the tablet terminal is foldable, the housing 9630 can be closedwhen the tablet terminal is not used. As a result, the display portion9631 a and the display portion 9631 b can be protected; thus, a tabletterminal having excellent durability and excellent reliability in termsof long-term use can be provided.

The tablet terminal illustrated in FIGS. 8A and 8B can have a functionof displaying a variety of kinds of data (e.g., a still image, a movingimage, and a text image), a function of displaying a calendar, a date,the time, or the like on the display portion, a touch-input function ofoperating or editing the data displayed on the display portion by touchinput, a function of controlling processing by a variety of kinds ofsoftware (programs), and the like.

The solar cell 9633 provided on a surface of the tablet terminal cansupply power to the touch panel 9800, the display portion, a videosignal processing portion, or the like. Note that the solar cell 9633can be provided on one or both surfaces of the housing 9630 and thebattery 9635 can be charged efficiently. The use of a lithium ionbattery as the battery 9635 is advantageous in downsizing or the like.

The structure and the operation of the charge/discharge control circuit9634 illustrated in FIG. 8B are described with reference to a blockdiagram in FIG. 8C. The solar cell 9633, the battery 9635, the DCDCconverter 9636, a converter 9647, switches SW1 to SW3, and a displayportion 9631 are illustrated in FIG. 8C, and the battery 9635, the DCDCconverter 9636, the converter 9647, and the switches SW1 to SW3correspond to the charge/discharge control circuit 9634 illustrated inFIG. 8B.

First, an example of the operation in the case where power is generatedby the solar cell 9633 using external light is described. The voltage ofpower generated by the solar cell is stepped up or down by the DCDCconverter 9636 so that the power has voltage for charging the battery9635. Then, when the power from the solar cell 9633 is used for theoperation of the display portion 9631, the switch SW1 is turned on andthe voltage of the power is stepped up or down by the converter 9647 soas to be voltage needed for the display portion 9631. In addition, whendisplay on the display portion 9631 is not performed, the switch SW1 isturned off and the switch SW2 is turned on so that the battery 9635 maybe charged.

Note that the solar cell 9633 is described as an example of a powergeneration means; however, there is no particular limitation on a way ofcharging the battery 9635, and the battery 9635 may be charged withanother power generation means such as a piezoelectric element or athermoelectric conversion element (Peltier element). For example, anon-contact electric power transmission module which transmits andreceives power wirelessly (without contact) to charge the battery 9635,or a combination of the solar cell 9633 and another means for charge maybe used.

By using a conductive oxide film having a crystal structure in whichc-axes are aligned in a direction perpendicular to a surface of the filmand having high conductivity and high transmittance of visible light ina touch panel, a solar cell, or the like, the electronic device can havehigh performance.

The structures, methods, and the like described in this embodiment canbe combined as appropriate with any of the structures, methods, and thelike described in the other embodiments.

This application is based on Japanese Patent Application serial no.2012-195401 filed with Japan Patent Office on Sep. 5, 2012, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A method for forming a conductive oxide filmcomprising the steps of: forming a conductive oxide film over asubstrate by a sputtering method at a substrate temperature of 200° C.or higher; and performing nitrogen annealing treatment on the conductiveoxide film.
 2. The method for forming a conductive oxide film accordingto claim 1, wherein the step of forming the conductive oxide film isperformed in an atmosphere including an argon gas.
 3. The method forforming a conductive oxide film according to claim 2, wherein apercentage of the argon gas is more than or equal to 70%.
 4. The methodfor forming a conductive oxide film according to claim 1, wherein atemperature in the nitrogen annealing treatment is higher than or equalto 350° C.